In order to measure the state of charge of primary batteries, it is usually necessary to measure the current or voltage of the battery under test. The testing of current and voltage is usually performed with external test equipment, such as voltmeters and battery testers. The cost of the associated test equipment or testers varies widely. There are digital multimeters which will measure both voltage and current as well as devices which utilize simple resistor calibrated galvometers. There is also heat sensing material which changes color when the material is heated up by an electrical conductor which is placed across the battery terminals. In all cases of the measurement of a primary battery, it has been necessary to place the battery either in or near the tester and then to initiated the test. in some tester devices, the placing of the battery in the tester itself causes electrical contact to be made with the battery which initiates the test. In other cases, external leads from the tester are connected to the battery terminals to initiate the test. In some cases, the state of charge reading is monitored continuously by the test device, but in most cases it is done briefly in order to provide a quick sampling of the state of charge of the battery.
The principal problem with all of these methods is that na external tester of some kind must be used to measure the state of charge of primary batteries. The battery alone will not render any state of charge information to the user.
In accordance with the disclosure of prior U.S. patents of the applicant, there is provided a battery charge indicator which is comprised of a first means to define a compressible chamber for battery charge indicator which is comprised of a first means to define a compressible chamber for containing a viscous gel and having an outlet therefrom as well as a second means to define a viewing channel of predetermined shape in communication with the outlet of the chamber in order to receive a flow of gel therefrom in an amount corresponding to a predetermined compression of the chamber. The battery charge indicator is incorporated into the battery, such as an alkaline battery, including a housing having an internally contained chemical cathode and anode for generating an electrical current with the cathode expanding in an amount proportional to the total current generated. The battery charge indicator is incorporated in the alkaline battery in such a manner that the compressible chamber is exposed to the cathode for compression thereby in response to an expansion of the cathode.
The cooperation between the battery charge indicator and the alkaline battery is such that when there is an electrical discharge from the battery, the internal components of the battery expand accumulatively as the battery discharges, thereby producing a force which can be used to operate the built-in battery charge indicator in order to indicate the enclosed expansion which is inversely proportional to the remaining electrical charge in the battery. Thus this battery charge indicator operates mechanically to amplify the expansion of the cathode in order to render a continuous sensitive visual state of charge indication. This battery charge indicator is typically installed at one end of the battery as a permanent part of the finished product. Further, this battery charge indicator is constructed in order to produce a visual indication of the state of charge in an analog manner.